Microsoft has made the Sender ID framework specification for e-mail authentication available to users at no cost and with the guarantee that it will never take legal action against them. The Sender ID specification will now be available to anybody wanting to use it under Microsoft's Open Specification Promise.

The move is part of an effort to promote interoperability among commercial and open-source software products, and among Internet access providers that utilize e-mail authentication, Microsoft said in a statement. "Users will be able to implement, commercialize and modify Microsoft's patented e-mail authentication technology without having to sign a licensing agreement," it said.

Sender ID is a caller ID-like system for e-mail meant to help fight spam and related cyberscams such as phishing. Microsoft has been pushing the technology for a couple of years as a partial solution to junk e-mail. Intellectual property issues around the technology have flared up in the past as a roadblock to adoption.